A Study of Differential Phase Delay of CE-3 based on Chinese VLBI Network

After its successful soft landing, Chinese VLBI Network has been observing Chang'E-3 Rover and Lander by using Same-Beam VLBI technique. In this paper, we present a research on the residuals of DPD after eighth-order polynomial fitting.Its random error is 0.085 picosecond (ps) as Rover transmits data and 0.192ps when rover launches telemetry signal. We also acquire closure delay of DPD; it almost equals to the systematic error that computes during determination, which implies that cycle ambiguity of DPD can be successfully determined. We also analyze the residuals obtained after relative position determination, and find that RMS is around 0.2-0.7mm when the rover transmits telemetry signal, and is about 0.05mm while rover transmits data. Based on the analysis of DPD residuals, we conclude that the system error of DPD has three main issues affecting its performance, including the bias of cycle ambiguity, the differential delay of ionospheric and the noise which is caused by the reference signal with low frequent stability.